Copy control information has been added to digital data to protect copyright of the digital data. For example, in the case of the DTCP (Digital Transmission Content Protection, see, e.g., Non-Patent Document 1), the copy control information is recorded as two-bit information in the CCI (Copy Control Information) transmitted concurrently with the stream or in the EMI (Encryption Mode Indicator) included in a packet header. The two-bit information specifies the following four types of the copy control. That is, the four types are Copy-free (copying is permitted without constrained condition), No-more-copies (recopying is prohibited), Copy-one-generation (copying is permitted only for one generation), and Copy never (copying is prohibited).
A stream specified to Copy-free can be recorded. A stream specified to Copy-one-generation can also be recorded by changing copy control information of the stream to No-more-copies. A stream specified to No-more-copies or Copy never cannot be recorded.
The BS digital broadcasting/CS digital broadcasting is operated in the same way (see, e.g., Non-Patent Document 2). The CCI or EMI corresponds to the digital recording control data included in the digital copy control descriptor transmitted concurrently with the stream. The digital recording control data are two-bit data and the value thereof specifies “copying is permitted without constrained condition”, “copying is permitted only for one generation”, and “copying is prohibited”. A pattern corresponding to “recopying is prohibited” is not prescribed in the broadcasts and such a case is construed as “copying is prohibited”.
For example, in the case of the CPRM (Content Protection for Removable Media), copyright of digital data are protected using the MKB (Media Key Block) and media ID recorded in an unwritable area of a recording medium, and device keys recorded in a recording device and a reproducing device.
FIG. 13 is a diagram for explaining a conventional technology relating to copyright protection of digital data. In FIG. 13, the MKB and media ID are recorded in an unwritable area of a recording medium. Both recording device and reproducing device secretly hold a device key. First, a process at the time of recording will be described. At (A), the recording device generates a media key from the device key and the MKB. At (B), the recording device generates a media unique key from the media key and the media ID. At (C), using the media unique key, the recording device encrypts a randomly generated title key. The encrypted title key is recorded on the recording medium. At (D), the recording device generates a key from the title key and the CCI. The CCI is not encrypted and is directly recorded on the recording medium. At (E), using the key generated at (D), the recording device encrypts data. The encrypted data are recorded in the recording medium.
A process at the time of reproducing will be described. At (A′), the reproducing device generates the media key from the device key and the MKB. At (B′), the reproducing device generates the media unique key from the media key and the media ID. At (C′), the reproducing device decrypts the encrypted title key read from the recording medium with the media unique key to acquire the title key. At (D′), the reproducing device generates a key from the title key and the CCI on the recording medium. At (E′), using the key generated at (D′), the reproducing device decrypts the encrypted data on the recording medium. Since the device key is secret, only a legitimate reproducing device can utilize the data. Although the encrypted title key and the CCI are recorded in the readable/writable area and can be changed, if one or both of the encrypted title and the CCI are illegally rewritten, the key acquired at (D′) becomes unauthorized and the encrypted data becomes unavailable.
On the other hand, along with development of portable terminals, the video data are increasingly recorded in a portable terminal and utilized outside. In this situation, the data once recorded in the recording device are dubbed into a portable terminal.
In Patent Document 1, a video/audio data recording/reproducing method and a disk device using the method are provided which enables a recorded moving image to be watched on a television and on a portable terminal easily by dubbing the same moving image onto a memory card, as follows.
That is, a disk medium records a first video/audio file that is made by compressing and converting a video/audio signal into a first video/audio format and a second video/audio file that is made by compressing and converting the video/audio signal into a second video/audio format different from the first video/audio format, and the disk medium records correlation information that can manage the first video/audio file and the second video/audio file as one content.
FIG. 14 is a block diagram of a configuration example of a conventional video recorder, and a video recorder 100 houses an HDD (hard disk drive) 109 that records video/audio files. The video recorder 100 includes a TV tuner 101 that is a video/audio signal receiving means receiving a TV signal input externally, an MPEG2 encoder 102 that is a first signal converting means converting the video/audio signal output from the TV tuner 101 into a format complying with the MPEG2 standard, an MPEG4 encoder 103 that is a second signal converting means converting the video/audio signal output from the TV tuner 101 into a format complying with the MPEG4 standard, and an HDD control circuit 104 that is a disk medium recording means recording the video/audio file into the HDD 109 after the conversion by the above two encoders.
The video recorder 100 includes an MPEG2 decoder 105 that converts (decompresses) the MPEG2 data recorded in the HDD 109 into a signal reproducible in a graphics circuit 108, a memory card control circuit 106 that can record/reproduce data into/from a memory card, and a CPU 107 that controls the blocks of the video recorder 100.    Non-Patent Document 1: Digital Transmission Content Protection Specification Volume 1 (Informational Version)    Non-Patent Document 2: ARIB (Association of Radio Industries and Businesses) ed., “Operational Guidelines for BS/Broadband CS Digital Satellite Broadcasting, Document No. ARIB TR-B15”, version 2.9, eighth edition, February 2004.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2003-179852